1. Field of the Invention
The present invention relates to a rubber composition for forming a core of a solid golf ball.
2. Description of the Related Art
Conventionally, there have been disclosed techniques for incorporating a metallic salt of an organic sulfur compound such as pentachlorothiophenol into a rubber composition for forming a core of a solid golf ball, to thereby enhance restitution of the core (see Japanese Patent Nos. 2669051, 2961735, and 2778229).
However, as described above, when a metallic salt of an organic sulfur compound is incorporated into a rubber composition for forming a core of a solid golf ball, the curing rate of the rubber composition is lowered, whereby a long time is required for curing the rubber composition, resulting in poor productivity of a core. Meanwhile, when an organic sulfur composition such as thiol or sulfide is incorporated into a rubber composition for forming a core (see Japanese Patent Application Laid-Open (kokai) No. 2001-187167), a long time is required for curing the rubber composition, and the resultant core exhibits unsatisfactory restitution.
In view of the foregoing, an object of the present invention is to provide a rubber composition for forming a core of a solid golf ball, which exhibits high curing rate, to thereby attain short curing time and improve productivity of a core, and which enables formation of a core of excellent restitution.
In order to achieve the above object, the present inventors have performed extensive studies, and have found that, when a mixture of a metallic salt of an organic sulfur compound and a metallic salt of an unsaturated carboxylic acid, the mixture being prepared by mixing particles of these metallic salts without employment of a solvent (hereinafter the mixture may be referred to as a xe2x80x9cdry blendxe2x80x9d), and/or a mixture of these metallic salts prepared by mixing particles of the salts in a poor solvent for the particles and then removing the solvent (hereinafter the mixture may be referred to as a xe2x80x9csolvent slurry blendxe2x80x9d) are incorporated into a rubber composition for forming a core of a solid golf ball, the curing rate of the rubber composition is increased.
The present invention has been accomplished on the basis of this finding. Accordingly, the present invention provides a rubber composition for a solid golf ball comprising a base rubber (A); a filler (B); an organic peroxide (C); and a dry blend and/or a solvent slurry blend (D) of an unsaturated carboxylic acid metallic salt and a metal-containing organic sulfur compound represented by the following formula (1): 
(wherein X represents a halogen atom, each of m and n represents an integer of 0 to 5 inclusive, and M represents a divalent metallic atom).
The present invention also provides a solid golf ball (specifically, a one-piece golf ball, or a multi-piece golf ball such as a two-piece golf ball or a three-piece golf ball) comprising a core formed from the rubber composition for a solid golf ball of the present invention.
The present invention also provides a method for producing a rubber composition for a solid golf ball comprising mixing a base rubber (A), a filler (B), an organic peroxide (C), a metal-containing organic sulfur compound (P) represented by formula (1), and an unsaturated carboxylic acid metallic salt (Q), wherein the metal-containing organic sulfur compound (P) represented by formula (1) is mixed with a portion or the entirety of the unsaturated carboxylic acid metallic salt (Q) in advance, to thereby prepare a blend (R); and the blend (R) is mixed with the base rubber (A), the filer (B), and the organic peroxide (C).
Preferably, the blend (R) is the aforementioned dry blend and/or solvent slurry blend (D)) of an unsaturated carboxylic acid metallic salt and a metal-containing organic sulfur compound represented by formula (1).